Set editor-wide portrait height and opacity in Preferences

[nagotown]

Acknowledgement

• I have read Getting-Started and FAQ

Description of the new feature / enhancement

It's a bit tiring to manually set the portrait (generally the fullbody image displayed in the piano roll if enabled) and opacity settings for each character.yaml individually, so it would be convenient to have a global setting for it.
Additionally, maybe portrait sizing could also support percentages similar to responsive sites as opposed to pixel amounts.

Proposed technical implementation details

No response